Gene activity and gene regulation of muscle specific genes will be investigated during myogenic differentiation in culture. The analysis of muscle specific genes will be facilitated by the use of available recombinant DNA probes. Filter hybridization with known probes, such as the empryonic muscle myosin heavy chain gene, will be used to investigate the developmental pattern of mRNA accumulation and transcription for a group of coordinately regulated genes. The specificity of the individual probes and the quantitative analysis of these developmental events will allow 'coordinate regulation' to be critically evaluated and facilitate the investigation of regulation at the gene level. Since some muscle genes of Drosophila melanogaster are clustered near many flightless mutants, cells containing these mutant genotypes will be placed in culture to investigate the regulation of coordinate gene systhesis and/or accumulation of specific myogenic proteins. The molecular level of the nutation's effect will be determined (transcription, processing, translation or degradation).